In late years, monitoring the human condition of a driver while driving has been drawing attention as a measure for preventing a traffic accident. For example, Patent Documents 1 to 3 disclose a technique to detect vibration on a body surface accompanying beating of the heart with a piezoelectric element (piezoelectric film sensor) in a thin film form attached to a cushion material forming a seat cushion. This technique is to monitor the human condition by chaos analysis of output of the piezoelectric element and does not require attaching of a large monitoring device to the head, allowing easy evaluation of the human condition of a driver.
Patent Document 1: Japanese Patent Application Laid-open No. H9-308614
Patent Document 2: Japanese Patent Application Laid-open No H10-146321.
Patent Document 3: Japanese Patent Application Laid-open No2005-168608.